1. Technical Field of the Invention
The present invention relates generally to an engine control system which may be employed in automotive vehicles and is designed to use an algorithm to control operations of actuators such as a fuel injector and an EGR (Exhaust Gas Recirculation) valve to regulate a combustion condition of fuel in an internal combustion engine and also to control output characteristics of the engine.
2. Background Art
Engine control systems are known which determine controlled variables such as the quantity of fuel to be injected into an engine (which will also be referred to as an injection quantity), the injection timing, the amount of a portion of exhaust gas to be returned back to the inlet of the engine (which will also be referred to as an EGR amount below), the boost pressure, the amount of intake air, the ignition timing, and an open/close timing of intake and exhaust valves to bring an engine output-related value such as the amount of exhaust emissions, for example, NOx or CO, the torque outputted by the engine, or the specific fuel consumption (or fuel efficiency) into agreement with a required value.
Most of the engine control systems are equipped with a control map which stores optimum values of, for example, a target quantity of fuel to be injected into the engine for respective required engine output-related values. The control map is usually made by adaptability tests performed by an engine manufacturer. The engine control systems work to calculate the controlled variable needed to meet the required engine output-related value using the control map and output a command signal to a corresponding actuator to achieve the controlled variable.
The making of the control map usually requires a huge number of adaptability tests, so that the adaptability tests consume a significant amount of time in total. The adaptability test work and map-making work, therefore, impose a heavy burden on control system manufacturers. Particularly, when the control map is made with respect to each of environmental conditions such as the temperature of engine coolant and the outdoor air temperature, it requires a large number of adaptability tests which will constitute a great burden on the control system manufacturers.
The adaptability tests are usually performed for each of the different engine output-related values. This is likely to result in interference between the different types of controlled variables in that when one of the engine output-related values reaches its required value, another engine output-related value deviates from its required value, while when the another engine output-related value is brought to the required value, the previously mentioned one of the engine output-related values deviates from the required one. It is, therefore, very difficult to bring the different types of engine output-related values into agreement with target values simultaneously.
Japanese Patent First Publication Nos. 2008-223643 and 2007-77935 disclose engine control systems which calculate a target value of pressure in a cylinder of the engine (i.e., a combustion parameter) based on a value of torque the engine is required to output and adjust the open/close timing of the intake and exhaust valves and the quantity of fuel to be injected into the engine (i.e., controlled variables of actuators) so as to bring the in-cylinder pressure into agreement with the target value.
The above engine control systems, however, also need to experimentally sample optimum values of the in-cylinder pressure for respective required values of output torque of the engine through the adaptability tests to make the control map, which will consume lots of time. The engine control systems also face the problem on the interference between the different types of controlled variables in that when an actual output torque of the engine reaches a required value, another engine output-related value such as the amount of NOx deviates from a target value, while when the another engine output-related value reaches the target value, the actual output torque deviates from the required value. It is, thus, difficult to bring the different types of engine output-related values into agreement with target values simultaneously.
The engine control systems of the above publications also have the following problem. Each of the actuators usually has an allowable operation range. For instance, a minimum possible amount of fuel the fuel injector can spray in a single injection event depends upon a limit of the speed at which the fuel injector is to be opened or closed. Consequently, even when the engine control systems output a command value to instruct the fuel injectors to spray less than the minimum possible amount, the fuel injectors will spray the minimum possible amount of fuel. Additionally, when the amount of fuel to be sprayed in the pilot injection event prior to the main injection event is increased excessively in a multi-injection mode in which the fuel is sprayed several times in each engine operating cycle (i.e., a four-stroke cycle) including intake or induction, compression, combustion, and exhaust, it may cause the amount of exhaust smoke to exceed an allowable value. It is, thus, necessary to give an upper limit to the amount of fuel to be sprayed in the pilot injection event. When the command values produced in the above-mentioned engine control systems are to instruct the fuel injectors to spray an amount of fuel which are outside the upper or lower limit (i.e., the allowable operation range, it may cause the engine output-related values to deviate from required values greatly.
Further, when it is required to operate the actuators to regulate the engine output-related values in response to a change in temperature of coolant for the engine, the limitation to the operation of the actuators within the allowable operation ranges may result in a failure in bringing the engine output-related values into agreement with required values, respectively.